Process combination of fluid coking and steam cracking

ABSTRACT

THIS INVENTION RELATES TO A FLUID COKING-STEAM CRACKING FURNACE COMBINATION PROCESS FOR PRODUCING COKE AND GASEOUS HYDROCARBONS FROM A HEAVY HYDROCARBON FEEDSTOCK WHEREIN A SUBSTANTIAL PORTION OF THE HEAT REQUIREMENTS FOR THE ENDOTHERMIC-CRACKING REACTION IN THE FLUID COKING VESSEL ARE MET BY PASSING STEAM THROUGH A FURNACE, PREFERABLY A STEAM CRACKING FURNACE, AND THEREAFTER INTRODUCING SAID HEATED STEAM INTO THE BOTTOM OF THE FLUIDIZED BED OF THE COKER VESSEL. IN ONE EMBODIMENT, STEAM IS FIRST HEATED IN A STEAM CRACKING FURNACE AND INTRODUCED INTO THE BOTTOM OF THE FLUID BED TO PROVIDE A SUBSTANTIAL PORTION OF THE HEAT REQUIREMENTS FOR THE CRACKING REACTION. THE REMAINING PORTION OF THE HEAT REQUIREMENTS FOR THE CRACKING REACTION ARE SUPPLIED BY EMPLOYING HEAT TRANSFER SURFACES WITHIN THE FLUID BED OF THE COKER VESSEL. HEAT IS SUPPLIED TO THE HEAT TRANSFER SURFACES BY PASSING A HOT MOLTEN MEDIUM, SUCH AS MOLTEN LEAD, OR HOT COMBUSTION GASES WITHIN SAID HEAT TRANSFER SURFACES. IN ANOTHER EMBODIMENT, THE HEAT REQUIREMENTS FOR THE ENDOTHERMIC CRACKING REACTION ARE SUPPLIED BY INTRODUCING STEAM, WHICH HAS BEEN HEATED IN A STEAM CRACKING FURNACE, INTO THE BOTTOM OF THE FLUID BED, AND WITHDRAWING CARBONACEOUS MATERIAL FROM THE FLUID BED AND CONTACTING SAID MATERIAL WITH HEAT TRANSFER SURFACES LOCATED IN AN EXTERNAL HEAT EXCHANGER TO PROVIDE THE REMAINING PORTION OF THE HEAT REQUIRED FOR THE CRACKING REACTION. THE INTRODUCTION OF STEAM INTO THE BOTTOM OF THE FLUID BED, IN ADDITION TO SUPPLYING A SUBSTANTIAL PORTION OF THE HEAT REQUIREMENTS TO THE FLUID BED, FUNCTIONS TO FLUIDIZE THE BED AND TO PROVIDE THE DILUENT MEDIUM FOR THE VAPORIZED HYDROCARBONS RECOVERED FROM THE FLUID BED COKING ZONE WHICH ARE THEN PASSED TO A STEAM CRACKING FURNACE TO PRODUCE THE LOW MOLECULAR WEIGHT UNSATURATED PRODUCTS.

PROCESS COMBINATION OF FLUID COKING AND STEAM CRACKING Filed Sept. 19, 1969 A ril 4, 1972 v B. WIRTH ETAL 2 shoots-Sheet 1 D E E F PRODUCT ll-ll'llll Fig. H0)

STEAM (FROM STEAM CRACKING FURNACE) INVENTORS G B W/rfh C. E. Ja/mig ATTORNEY A ril 4, 1972 B. WIRTH EIAL 3,654,134

PROCESS COMBINATION OF FLUID COKING AND STEAM CRACKING Filed Sept. 19, 1969 i 2 Sheets-Sheet 2 B. Wirlh C. E. Jfl/Mig NVENTORS a BY ATTORNEY United States Patent *(lihce 3,654,134 Patented Apr. 4, 1972 Cl. 208-54 26 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a fluid coking-steam cracking furnace combination process for producing coke and gaseous hydrocarbons from a heavy hydrocarbon feedstock wherein a substantial portion of the heat requirements for the endothermic-cracking reaction in the fluid coking vessel are met by passing steam through a furnace, preferably a steam cracking furnace, and thereafter introducing .said heated steam into the bottom of the fluidized bed ofthe coker vessel. In one embodiment, steam is first heated in a steam cracking furnace and introduced into the bottom of the fluid bed to provide a substantial portion of the heat requirements for the cracking reaction. The remaining portion of the heat requirements for the cracking reaction are supplied by employing heat transfer surfaces within the'fluid bed of the coker vessel. Heat is supplied to the heat transfer surfaces by passing a hot molten medium, such as molten lead, or hot combustionvgases within said heat transfer surfaces. In another embodiment, the heat requirements for the endothermic cracking reaction are supplied by introducing steam, which has been heated in a steam cracking furnace, into the bottom of the fluid bed, and withdrawing carbonaceous material from the fluid bed and contacting said material with heat transfer surfaces located in an external heat exchanger to provide the remaining'portion of the heat required for the cracking reaction. The introduction of steam into the bottom of the fluid bed, in addition to supplying a substantial portion of the heat requirements to the fluid bed, functions to fluidize the bed and to provide the diluent medium for thevaporizcd hydrocarbons recovered from the fluid bed coking zone which are then passed to a steam cracking furnace to produce the low molecular weight unsaturated products.

BACKGROUND THE INVENTION This invention relates to an improved fluid cokingsteam cracking furnace process combination for the thermal cracking. of a heavy hydrocarbon feedstock and residual feeds wherein the feedstock is introduced into a fluid b ed of hot carbonaceous particles to form carbonaceous materials, i.e. coke, hydrogen and gaseous, hydrocarbonproducts. More particularly, 7 this invention relates to a. fluid coking-steam cracking combination, process wherein a substantial portion of the heat requirements. for the endothermic cracking reaction of the heavy hydrocarbon feedstock in the fluid bed is supplied by passing steam through a furnace, preferably through a steam cracking furnace, to heat said steam to a temperature in the range of from about 120-0" F. to about 1900 F, In one embodiment, steam is heated in a steam cracking furnace and introduced into the bottom portion of the fluid coker containing the fluid bed in order to provide a substantial portion of the heat requirement for theendothermic crackingreaction occurring therein, The remaining portion of the heat requirements'tothc fluid bed are met by employing heat transfersurfaces comprisingv cylindrical ,pipes which are submerged in the fluid coke bed. The heat transfer surfaces are heated either by passing a hot molten medium such as molten lead Within said heat transfer lines or by passing hot combustion gases within said heat transfer surfaces to affect a heat transfer from the heat transfer surfaces to the bed. In another embodiment of the instant invention, steam is heated in a steam cracking furnace and introduced into the bottom of the fluid bed to supply a substantial portion of the heat requirements to said bed, the remaining portion of the heat requirements for the cracking reaction in the fluid bed being obtained by removing a portion of the carbonaceous materials from the fluid bed and contacting said material with heat transfer surfaces located externally from the bed. The heat transfer surfaces normally comprise cylindrical pipes wherein the heat required to eifect the transfer of heat to said carbonaceous materials is provided by circulating within said pipes a molten medium such as molten lead or combustion gases such as the combustion products of natural gas with air or oxygen. After the materials are withdrawn from the fluid bed and contacted with the heat transfer surfaces, they are then recycled to the bed to impart the remaining portion of the heat required to effect the cracking of the hydrocarbon feedstocks in the fluid bed. In both of the above-described embodiments, in addition to supplying a substantial portion of the heat requirements to the fluid bed, the introduction of steam into the bottom portion of the bed serves to fluidize the bed and to provide diluent steam, i.e. the carrying and cracking medium, before passing the vaporized hydrocarbon recovered from the fluid bed coking zone, which vaporized hydrocarbon-steam mixture is then passed through a steam cracking furnace to produce the desired low molecular weight unsaturated products.

DESCRIPTION OF THE PRIOR ART It is well known in the art to prepare coke and gaseous hydrocarbon products in a fluidized process at temperatures between about 800 F. to 1100 F. In a typical fluid coking process, a hydrocarbon feed is injected into a reactor containing a hot fluidized bed of carbonaceous particles. The hydrocarbon is cracked to form solid coke which deposits on the existing carbonaceous particles, enlarging them in size. To maintain the desired particle size in the bed, smaller seed coke is added which may be obtained by comminuting part of the product coke, or steam-jet attriters can be employed in the coker. Vapors containing partially cracked hydrocarbons and hydrogen are also liberated. Heat for the endothermic cracking reactions is supplied by circulating coke particles from the reactor to an external heater or burner vessel wherein they are heated to a temperature generally ranging from about F. to 400 -F. above the temperature in the cracking zone and thereafter returned to the fluid bed of the reactor.

In UJS. 2,905,733, a process is described wherein a fluid coking system is combined with a steam cracking furnace in order to crack heavy residual feeds to low molecular weight products and carbonaceous materials. The process described in US. 2,905,733 consists of first cracking the heavy hydrocarbon oils by contacting them with heat-carrying solids to remove substantially all of the coke-forming material, and thereafter further cracking the vaporized product by contacting the said vaporized prodnet with super heated steam and thereafter passing said mixture through a steam cracking furnace. The heat requirements for the thermal cracking in the fluid bed are supplied by a stream of preheated solid particles which are heated in an external burner system. Steam may be introduced into the bottom of the bed in order to fluidize the system. The vaporized products which are recovered from the coking bed and which pass overhead from the coker vessel are thereafter contacted with an external source of superheated steam in order to provide the carrying and cracking medium, i.e., diluent, for the passage of said gaseous hydrocarbon-steam mixture through the steam cracking furnace.

SUMMARY OF THE INVENTION It has now been discovered that improved thermal efficiency can be realized in a fluid coking process combined with a steam cracking furnace wherein steam, having first been heated in a steam cracking furnace, is introduced into the bottom of the fluid bed of hot carbonaceous particles in a fluid coker to: (a) supply a substantial portion of the heat requirements directly to the cracking zone; (b) fluidize the bed of hot carbonaceous particles; and (c) provide diluent steam, i.e. the carrying and cracking medium for the vaporized hydrocarbons recovered from the cracking zone which are subsequently passed through a steam cracking furnace to produce low molecular weight unsaturated hydrocarbon products.

In one embodiment of this invention, steam is first passed through a steam cracking furnace to heat the steam to a temperature in the range of from about 1200 F. to about 1900 F. and more preferably from about 1400 F. to 1600 F. The pre-heated steam is then introduced into the bottom of the bed to fluidize the bed, provide diluent steam and supply a substantial portion of the heatrequirements for the cracking reaction in the bed. The remaining portion of the heat requirement for the cracking reaction which occurs in the bed is supplied by employing heat transfer surfaces, for example cylindrical pipes, within the fluid bed. Molten media such as molten lead or hot combustion gases are circulated through said transfer surface in order to supply the remaining portion of the heat required to maintain the bed at about 800 F. to about 1200 F. and preferably from about 900 F. to 1000 F.

In another embodiment of the instant invention, steam, which is passed through a steam cracking furnace such that the steam is heated to a temperature of from about 1200 F. to about 1900 F. is introduced into the bottom of the fluid bed to supply a substantial portion of the heat requirements to said bed. The remaining portion of the heat requirement to said bed is supplied by removing carbonaceous particles from said bed and contacting said carbonaceous particles with heat transfer surfaces located externally to said bed. The heat transfer surfaces which may comprise cylindrical pipes are heated by passing a molten media or hot combustion gases on one side of said cylindrical pipe. After contact with the heat transfer surfaces, the carbonaceous particles are then recycled to the bed to supply the remaining portion of the heat required for the cracking reactions.

As previously mentioned, vaporized hydrocarbons along with steam are recovered from the cracking zone and are passed directly to a steam cracking furnace. The vaporized hydrocarbons and steam are first heated in the convection section of a steam cracking furnace to a temperature in the range of from about 900 F. to 1300" F. Thereafter, the products from cracking zone are passed to the radiant zone of a steam cracking furnace where the steam cracking reaction occurs. Here the products in the radiant section are heated to a temperature of from about 1300 F. to about 1600 F. The residence time in the cracking zone ranges from about 0.1 to 1.0 second, preferably 0.3 to 0.7 second, the higher the temperature, the lower the residence time to obtain a given conversion level. Pressures within the tubes are not critical to the process and can range from about to about p.s.i.g. at the coil outlet, but higher pressures, e.g. up to 50 p.s.i.g. at the coil outlet, can be tolerated at some sacrifice in olefin yield. In order to optimize the yield of low molecular weight unsaturated hydrocarbon products, low hydrocarbon partial pressures are desirable. Steam, which is recovered from the cracking zone of the fluid bed coker 4 along with vaporized hydrocarbons, is an effective diluent for this purpose such that vaporized hydrocarbon feed which is fed to the steam cracking furnace is comprised of from about 10 to 50 weight percent steam and more preferably 25 to 40 weight percent steam.

In accordance with the practice of the instant invention, the heavy hydrocarbon feedstock is introduced into the upper portion, i.e. scrubber section, of a coker vessel. The feed may be introduced at ambient temperature or may be first preheated to a temperature in the range of from about 500 F. to about 900 F. and more preferably from about 700 F. to 850 F., by passing the feed through preheat exchangers or the convection section of a steam cracking furnace. Exemplary hydrocarbon feeds which can be employed in the practice of this invention include, but are not limited to, heavy hydrocarbon oils such as atmospheric and vacuum still crude residual, whole crude, tars and pitches. Typically, such feeds have an initial boiling point of about 700 F., preferably about 900 F. and an API gravity of about 0 to 20, and a Conradson carbon content of about 3 to 40 weight percent. The amount of coke formed from such feeds depends on the character of the material being processed and to some extent upon the coking conditions. In the case of a high Conradson carbon feedstock, the coke yields can be 50 weight percent or higher based on the residuum.

The lower boiling components of the hydrocarbon feed which are introduced into the upper portion, i.e. scrubber section of the coker vessel, are vaporized by the gases passing upwardly from the fluidized bed of hot carbonaceous particles such that the product vapors which pass overhead from the coker vessel contain steam, the light fractions of the feed together with the lighter portions of the gas vapors passing upwardly through the fluidized bed. The light hydrocarbon fractions passing overhead contain cracked products such as ethylene and other gaseous hydrocarbons and vapors, exemplified by the components of a light naphtha and gas oil fraction. These light fractions, along with steam, are passed directly to the furnace of a steam cracking :unit where they are further cracked to form valuable low molecular weight unsaturates such as light olefins, exemplified by ethylene, propylene, butylene, butadiene, isoprene, as well as aromatics such as benzene, toluene, xylene and the like, which products are then further processed for the recovery of light products and distillate oils. The heavy, unvaporized fractions of the initial hydrocarbon feeds, along with the heavy condensed components of the vapors from the fluidized bed fall to the bottom of the scrubber and may be fed to the convection section of a steam cracking furnace before being passed to the fluid bed coking zone.

The vaporized products liberated in the coking zone by the thermal cracking process pass upwardly from the bed to a cyclone and into the scrubber section, i.e. upper portion of the coker vessel. Cyclone separators are a well known means for separating gases and solids from gas solid suspensions. The coke laden gas is passed upwardly from the coking zone and into a cyclone separator, separating essentially all of the coke particles which then pass as a dense phase to a standpipe or dipleg from the bottom of the cyclone back into the fluid bed of the cracking reactor. The gases leave the top of the cyclone at high temperatures and function in the instant process to vaporize the light ends of the hydrocarbon fieed which have been introduced into the scrubber section as described above.

The heat for carrying out the endothermic coke reaction is, in accordance with the instant invention, generated in an integrated steam cracking'unit formed by heat transfer surfaces such that the steam, having passed through a steam cracking furance, supplies a substantial portion of the heat requirements to the coker vessel. As discussed above, the steam is first heated in a steam cracking furnace to a temperature in the range of from about 1200 F. to about 1900 F. Thereafter, the remaining portion of the heat required to maintain the fluid bed in a heat balance of between about 800 F. to about 1100 F. and more preferably from about 900 F. to about 1000 F. is supplied either by: (a) employing heat transfer surfaces within the fluid bed, wherein said heat transfer surfaces, e.g. cylindrical pipes and are heated by circulating a hot molten medium such as molten lead or a hot combustion gas through saidheattransfer surfaces; or (b) by withdrawing a portion of the carbonaceous material from the fluid bed and contacting said carbonaceous material at a point external to the fluid bed with the heat transfer surfaces wherein the heat transfer surfaces are heated as described in embodiment (a). When either embodiment (a) or (b) are employed to supply the heat requirements for the cracking reaction, the amount of heat expressed in B.t.u.s supplied by the steam cracking furnace is in the range of from about 20 to about 80% and more preferably from about 40 to about 60% of the process heat required to maintain the heat balance required in a fluid coker. The temperature of the heat transfer surface, which surface supplies the remaining portion of the process heat to the cracking zone, is in the range of from about 1000 F. to about 1600" F. and preferably from about 1200" F. to about 1500" F. The heat transfer surfaces are maintained at such a temperature by circulating molten media such as molten lead, bismuth, cadmium, zinc, tin or alloys including these metals as Well as molten salts and the like or hot combustion gases such as the combustion products of fuel gas and oxygen containing gases such as air within the cylindrical pipe which comprises the heat transfer surface. The carbonaceous material which is withdrawn from the fluid bed is contacted with said external heat transfer surfaces for a period of time suflicient to heat the carbonaceous particles to a temperature of from about 1000 F. to about 1400 F. and more preferably to a temperature of about 1100" F. to 1200 F. The hot carbonaceous particles which are withdrawn from the fluid bed are transferred to the heat exchange zone containing the heat transfer surfaces and recycled back to the fluid bed by employing a lift gas or steam. The amount of lift gas or-steam employed is in the range of from about 0.005 to 0.04 pound of lift gas or steam per pound of hot carbonaceous material withdrawn from the bed and circulated. The amount of coke circulated may range from about 0.4 to 4.0 pounds per pound of oil feed to the coking zone, preferably in the range of from 1 to about 2.

Preferably, the steam is introduced below the fluidized bed in the conical shaped portion of the coker vessel. The amount of steam which is introduced in either embodiment (a) or (b) is in the range of from about 0.1 to 1.0 pound of steam and more preferably from about 0.3 to 0.6 pound of steam per. pound of feedstock on a coke-free basis. The -ratio .of amount of steam which is introduced into the bottomlof the fluid bed as compared with the amount of steam which may be. employed to lift the hot carbonaceous particles through the external heat transfer zone as described above in embodiment (b) is in the range of from 500 to land more preferably from 30 to 1. It should be noted that the vapors leaving the coking zone usually comprise from about 10 to 50 weight percent steam, and more preferably from about 25 to 40 weight percent steam, which steam has first beenv passed through a steam cracking furnace/The velocity of the steam in the bottom of the fluid bed is in. therange of from about 0.7 to 3.5 ft./ sec. The conical shaped portion of the coker vessel into which the st'eam'is introduced ,is refractory lined and a grid of refractory or metal separates the fluidized bed from the conical portion of thereactor vessel. The grid allows a uniform flow'of steam across the bottom of the coker vessel and produces uniform agitation and fluidization of the coke particles. A standpipe protrudes through the grid into the fluid coking portion of the reactor vessel and extends outwardly down through the conical portion of the reactor vessel through which carbonaceous material,

ie kejs'rerrioyed from thecoker yessehA ltcrnatively,

the coke may be withdrawn above the grid through the side wall of the reactor vessel. A portion of this coke is recirculated for heating as described above, and a portion is withdrawn as net product. It should be clear that the advantages of the present process are likewise present when well-known external burner systems are employed in place of embodiment (b) of the instant process.

The coke which is removed from the standpipe as described above is passed into a calciner to form the product coke. The calciner also contains a fluidized bed of carbonaceous particles into which the coke from the coker vessel passes. The bed of carbonaceous particles i.e. coke in the calciner is fluidized and heated by burning a fuel with an oxygen-containing gas, i.e. of natural gas and oxygen in a burner from which hot combustion products are injected within the upper two feet of the bed. This calciner bed is operated at a temperature from about 2000 to 2600 F., preferably from about 2300 to 2400 F. and serves to remove volatiles from the coke. At the same time, the density and electrical conductivity of the carbonaceous particles increase markedly, making the coke suitable as a raw material for making electrodes such as are used in electric furnaces and electrolytic production of aluminum. The coke is held at calcining temperature for from about A to about 2 hours.

The calcined coke product is withdrawn through a standpipe which communicates with the bed of fluidized coke particles. The gasesfrom the fluidized bed of the calciner are passed through a cyclone, similar to that described above for the fluid coker, pass overhead from the calciner to a heat exchanger and ultimately to a separator where the flue gas and volatiles from the coke are separated from entrained coke fines and water.

In another embodiment of this invention, the coke passing from the coker vessel is introduced into a fluidized bed of carbonaceous particles in the calciner as described above. In this embodiment, the coke product is withdrawn through a standpipe from the fluidized bed, contacted for a short time with hot steam which has been passed through a steam cracking furnace and further heated with hydrogen-oxygen burners to increase the temperature of the steam to a range of from about 2100 to 3200 F. This heats the coke particles to a temperature equal to or above that temperature existing in the fluid calciner bed, e.g. 2000 to 2600 F. These coke particles are then recycled into the upper portion of the calciner and passed through a cyclone such that the hot steam and volatiles from the coke may be recycled to the fluidized bed of the coker vessel and the coke back to the calciner. The coke product is removed from the standpipe emanating from the bottom of the calciner before said coke particles are contacted with steam in the presence of the hydrogen-oxygen burners. The contact time of the coke with steam is held to no more than about .2 to about 2 seconds, so that undesirable reactions are minimized.

This invention will be more clearly understood by reference to the accompanying drawings wherein:

FIG. 1 shows a suitable method and apparatus of first cracking a residual feed in a coker vessel, and then cracking the resulting vapors in an integrated steam cracking unit;

FIG. 2 shows the calciner from which the coke particles from the coker vessel are calcined to make product coke; and

FIG. 3 shows a modification of the calciner whereby the volatiles from the coke may be recycled directly back to the fluid bed of the coker vessel.

Referring first to FIG. 1, a heavy hydrocarbon feed stock such as an atmospheric residuum is fed to an inlet line 1 into the upper portion, i.e. scrubber section 2 of the coker vessel 3. The coker vessel may be operated at or near atmospheric pressure preferably at a moderate pressure of from about 20 to about p.s.i.g. The hydrocarbon feed is contacted inthe scrubber section with vapors passing upwardly from thefluidizedbed of the cokerfi,

to cyclone 5. The vapor contacts the hydrocarbon feed in the scrubber section 2 such that the light fractions of the hydrocarbon feed are vaporized and passed overhead 6 along with steam and light gases from the fluidized bed to the steam cracking furnace 7 which is operated at an outlet temperature of from about 1300 to about 1600" F. The steam cracked products are removed from the steam cracking furnace 7, quenched 8, and subsequently removed.

The heavy portion of the hydrocarbon feed which is not vaporized falls to the bottom of the scrubber section of the coker vessel along with the heavy condensed fractions of the vapors from the fluidized bed. These heavy fractions may then be removed by way of line 9, passing to a pump 10 which supplies suitable pressure to pass it through line 11 to the fluidized bed portion 4 of the coker vessel. Alternatively, pump 10 may supply suitable pressure to pump the heavy ends settling at the bottom portion of the scrubber section to line 12 of the convection section of the steam cracker 13. The temperatures at which the heavy fractions leave the scrubber section are in the range of from about 500 to about 900 F. After passing through the convection section of the steam cracker 13, the heavy ends are returned to the fluidized bed 4 by way of line 14 at a temperature below about 950 F.

Steam is passed by way of line 15 through the radiant section 16 of the steam cracking furnace. After the steam has been heated in the steam cracking furnace 16 to a temperature in the range of from about 1200 to about 1900 B, it is passed along line 17 into the conical shaped portion 18 of the coker vessel. The steam introduced into the conical shaped portion 18 of the coker vessel passes upwardly through the grid 19 to uniformly fluidize the bed, provide diluent steam for the subsequent steam cracking the overhead product 6 in the steam cracking furnace and to supply a substantial portion of the heat requirements for the coking process. A standpipe 20 extends from the fluidized bed portion of the reactor vessel 4 through the conical shaped portion of the reactor vessel 18 and passes outwardly carrying the coke to be calcined by way of line 21.

The remaining portion of the heat required for the cracking reaction in the fluid bed is supplied by heat transfer surfaces 22 located in the fluid bed portion 4 of the coker vessel 3. Heat is supplied to the heat transfer surfaces by Way of line 23 and 24 by circulating within said heat transfer surfaces either a molten media such as molten lead, or by hot combustion gases formed by burning a fuel such as natural gas with air or oxygen. The molten media circulated within heat transfer surfaces 22 are heated in a furnace 25.

An alternative embodiment of this invention, described above as embodiment (b), is exemplified by the drawing in FIG. 1(b) wherein steam from a steam cracking furnace (not shown) is passed by way of line 26 to the coker. The major portion of the steam from the steam cracking furnace, in excess of 90% of the steam passed by way of line '26, is introduced into the conical shaped portion of the coker vessel 27 by way of line 28. The steam introduced by way of line 28 functions to supply a substantial portion of the heat requirements to the fluid bed 29, to fluidize the bed and to provide diluent stream for carrying the overhead product recovered from the scrubber section as shown in FIG. 1(a). The remaining portion of the heat requirements to the fluid bed is supplied by removing carbonaceous materials from the fluid bed 29 by the way of standpipe 30 and injecting a lift gas 31 which may be a portion of the steam passed by way of line 26 which was not introduced into the conical shaped portion of the coker vessel 28 in order to transmit the carbonaceous particles to the heat transfer surfaces 32 by way of line 33. Heat is supplied to the heat transfer surfaces by circulating a hot molten media such as molten lead or a hot combustion gas in contact with said heat transfer surfaces 32. Heat is continuously applied to the molten media or combustion gases by circulating said media wih a furnace (not shown) such that the hot media or combustion gases enter the heat exchanger 34 from the furnace and exit to the furnace by way of lines 36. The carbonaceous particles which were removed from the coker bed by way of line 30 are contacted with said heat transfer surfaces 32 to raise the temperature of the carbonaceous particles i.e. coke to a temperature in the range of from about 1000 F. to about 1400 F. and more preferably in the range of from about 1100 to 1200 F. The then heated coke is transferred from the heat exchanger 34 by the way of line 35 and reintroduced into the fluid bed 29 to supply the remaining portion of the heat for the coking reactants.

In FIG. 2, the coke particles passing through line 21 are introduced into a fluidized bed of coke particles 37 in calciner 38. Submerged burners 39 and 40 inject the hot combustion products of an oxygen-containing gas and a fuel, i.e. natural gas-oxygen within one foot of the upper surface of the fluid coking bed to supply the, heat requirements needed for the calciner. The upflowing stream of vapors and carbonaceous solids are passed into the cyclone separator 41. The vapors are separated and taken overhead through line 42. The vapor is then passed through a heat exchanger 43 and into a separator 44 by way of line 45. The separator, i.e. fractionation zone, causes the flue gas and volatiles from the coke to pass overhead to line 46, while the coke fines, water, etc., are purged through line 47. The calcined product coke is removed from the fluidized bed of coke particles 37 through standpipe 48.

In FIG. 3, an alternative embodiment of the calciner is described. The coke passing from the coker vessel by way of line 21 passes into the fluidized bed of g the calciner 49. The coke particles are removed from the fluidized bed by Way of line 50 and are contacted with steam, which passes from a steam cracker (not shown) by way of line 51 and hydrogen and oxygen burners 52, to increase the temperature of the coke particles to about 2400 F. The vapors and solids therein are passed through a cyclone separator 53. The vapors including the volatiles from the coke particles and the hot steam are separated from the coke and taken overhead by way of line 54 and are recycled to the fluidized bed of the coker vessel. The calcined coke product is removed by way of line 35.

What is claimed is:

1. In a fluid coking process wherein a heavy hydrocar bon feedstock is cracked in a coking zone containing a fluidized bed of hot carbonaceous particles to produce hydrocarbon vapors and to deposit carbonaceous materials on said particles and wherein the hydrocarbon vaports are recovered from the coking zone and are passed along with diluent steam through a steam cracking furnace to produce low molecular weight unsaturated hydrocarbons, the improvement which comprises passing steam through a furnace to heat said steam and thereafter introducing said heated steam to the bottom of the coking zone to provide from about 20 to about percent of the heat requirements for said coking zone and to provide all of the diluent steam for the hydrocarbon vapors recovered from the coking zone which are passed to the steam cracking furnace. I

2. The process of claim 1 wherein said steam is heated to a temperature in the range of from about 1200 to about 1900 F. v

3. The process of claim 1 wherein said heavy hydrocarbon feedstock has a boiling point above about 600 F.

4. The process of claim 1 wherein said coking zone is maintained at a temperature in the range of from about 700 to about 1100 F.

5. A process for producing carbonaceous material and low molecular weight unsaturated hydrocarbons which comprises:

(a) introducing a heavy hydrocarbon feedstock into the upper portion of a coker vessel, said coker vessel comprising a scrubber zone and a coking zone containing a fluid bed of hot carbonaceous particles, and vapor and liquid passages connecting said zones;

(b) passing steam through a steam cracking furnace to heat said steam and thereafter introducing said heated steam into the' bottom of the. fluid bed to supply from about 20 to about 80% of the heat requirements for the'coking zone and to provide all of the .diluent steam for the I hydrocarbon vapors which are subsequently passed to a steam cracking furnace, the remaining portion of the heat requirements to the coking zone supplied by contacting the carbonaceous particles with' heat transfer surfaces located within the fluid bed;

(c) recovering as product vapors from the scrubber zone of the coker vessel the light fractions of the vapors passing from the coking zone, the lower boiling components of said feedstock vaporized in said scrubber zone by contact. with said vapors passing from the ,coking zone and steam;

(d) passing said product vapors through a steam cracking furnace, said steam .cracking furnace operated at V a temperature above about 1200 F. to produce low molecular. weight unsaturated hydrocarbons;

, (e) recovering a liquid from the scrubber zone comprising the unvaporized fractions of the hydrocarbon I feedstock and the condensed components of the vapors passing from the coking zone formed in step r (f) introducing said liquid recovered in step (e) into the coking zone.

The process of claim wherein said heavy hydrocarbon feedstock has a boiling point above about 600 F.

7. The process'of claim 5 wherein said feedstock is first preheated to a temperature in the range of from about 500 to about 950 F. before being introduced into the upper portion of the coker vessel.

' 8. A process of claims wherein said steam is heated to a temperature in the range of from about 1200 to about 1900 F. and is introduced into-the bottom of the fluid bed to supply from about 20 to about 80 percent of the heat requirements for the coking zone.

9. The process of claim 8 wherein said steam provides from about 40 to about 60% of the heat requirements for the coking zone.

10. The process of claim 5 wherein the temperature of the coking zone is maintained in the range of from about 700 to about 1100 F.

11. The process of claim 5 wherein the temperature of said heat transfer surfaces is in the range of from about 1000 to about 1600 F.

12. The processof claim 11 wherein the temperature of the heat transfer surfaces is maintained by passing a hot molten media within saidsurfaces.

13. Theprocessof claim 12 wherein said hot molten medium is molten lead.

3 14. The process of claim 11 wherein the temperature of said heat transfer surfaces is maintained by passing a hot combustion gas within said surfaces.

15. The process of claim 5 wherein carbonaceous material is withdrawn from the coking zone and introduced into a calciner, said calciner containing a fluidized bed of hot carbonaceous material, wherein the heat requirements fo'r the fluid bed in the calciner are provided by injecting the combustion products of an oxygen-containing-combustion gas burner within one foot of the upper surface of said b'edfand withdrawing carbonaceous material from said bed asproduct cokeh 1 16. The process of claim ,5 wherein carbonaceous material is withdrawn frornthe coking zone and introduced into a calciner containing afluid bed of hot carbonaceous material, withdrawing the carbonaceous material from said bed and contacting said withdrawn carbonaceous material'with a steam, wherein said steam is'first heated in a furnace" and thereafterjcontacted withfa sufficient amount of an oxygen-containing combustion gas mixture to provide the remaining portion of the heat required to raise the temperature of the carbonaceous material to about 2400 F., separating and recovering the vapors resulting from said contact of the carbonaceous materials with the steam and introducing said vapors to the coking zone of the coker vessel.

17. A process for producing carbonaceous material and low molecular weight unsaturated products which compr1ses:

(a) introducing a heavy hydrocarbon feedstock into the upper portion of a coker vessel, said coker vessel comprising an upper scrubber zone and a lower coking zone containing a fluid bed of hot carbonaceous particles, and vapor and liquid passages connecting said sections;

(b) passing steam through a steam cracking furnace to heat said steam and thereafter introducing said heated steam into the bottom of the fluid bed to supply from about 20 to about of the heat requirement for said coking zone and to provide all of the diluent steam for the hydrocarbon vapors recovered from said coking zone which are subsequently passed to a steam cracking furnace, the remaining portion of the heat requirement to the coking zone supplied by removing the carbonaceous particles from said cokink zone and contacting said carbonaceous particles with heat transfer surfaces located externally from said coking zone and thereafter returning said carbonaceous particles to the coking zone;

(c) recovering as product vapors from the scrubber section of the coker vessel and light fractions of the vapors passing from the coking zone, the lower boiling components of said feedstock vaporized in said scrubber zone by contact with said vapors passing from the coking zone and steam;

(d) passing said product vapors through a steam cracking furnace, said steam cracking furnace operated at a temperature above about 1200 F. to produce low molecular weight unsaturated hydrocarbons;

(e) recovering a liquid from the scrubber zone comprising the unvaporized fractions of the hydrocarbon feedstock and the condensed components of the vapors passing from the coking zone formed in step (c); and

(f) introducing said liquid recovered in step (e) into the coking zone.

18. The process of claim 17 wherein said heavy hydrocarbon feedstock has a boiling point above about 600 F.

19. The process of claim 17 wherein said feedstock is first preheated in the steam cracking furnace before being introduced into the upper portion of the coker vessel and wherein said steam provides from about 40 to about 60% of the heat requirement for said coking zone.

20. The process of claim 17 wherein said steam is heated in the steam cracking furnace to a temperature in the range of from about 1200 to about 1900 F. and wherein said heated steam is introduced into the bottom of the fluid bed to supply from about 20 to about 80 percent of the heat requirements for the coking zone.

21. The process of claim 17 wherein the temperature of the cracking section is maintained in the range of from about 700 to about 1100 F.

22. The process of claim 17 wherein the liquid recovered from the scrubber zone is preheated in the steam cracking furnace before being introducedrinto the coking zone.

23. The process of claim 17 wherein the oxygen-containing combustion gas mixture consists essentially of hydrogen and oxygen.

24. The process of claim 17 wherein the oxygen-containing combution gas mixture consists essentially of natural gas and oxygen.

25. The process of claim 17 wherein carbonaceous material is withdrawn fro m the coking-zone and introduced into a calciner, said calciner containing a fluidized bed of hot carbonaceous material, wherein the heat requirements for the fluid bed in the calciner are provided by injecting the combustion products of an oxygen-containing combustion gas burner within one foot of the upper surface of said bed, and withdrawing carbonaceous material from said bed as product coke.

26. The process of claim 16 wherein carbonaceous material is withdrawn from the coking zone and introduced into a calciner containing a fluid bed of hot carbonaceous material, withdrawing the carbonaceous material from said bed and contacting said withdrawn carbonaceous material with steam, wherein said steam is first heated in a steam cracking furnace and thereafter contacted with a suflicient amount of an oxygen-containing combustion gas mixture to provide the remaining portion of the heat required to raise the temperature of the carbonaceous material to about 2400" F., separating and recovering the vapors resulting from said contactof the carbonaceous materials with the steam and introducing said vapors to the coking zone of the coker vessel.

References Cited V UNITED STATES PATENTS Smith et a1. 208-127 HERBERT LEVINE, Primary Examiner I Us. c1. X.R. 20s 127, 130 

